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package org.apache.juneau.http;

/**
 * Represents a parsed <l>ETag</l> HTTP response header.
 * 
 * <p>
 * An identifier for a specific version of a resource, often a message digest.
 * 
 * <h5 class='figure'>Example</h5>
 * <p class='bcode'>
 * 	ETag: "737060cd8c284d8af7ad3082f209582d"
 * </p>
 * 
 * <h5 class='topic'>RFC2616 Specification</h5>
 * 
 * The ETag response-header field provides the current value of the entity tag for the requested variant.
 * The headers used with entity tags are described in sections 14.24, 14.26 and 14.44.
 * The entity tag MAY be used for comparison with other entities from the same resource (see section 13.3.3).
 * 
 * <p class='bcode'>
 * 	ETag = "ETag" ":" entity-tag
 * </p>
 * 
 * <p>
 * Examples:
 * <p class='bcode'>
 * 	ETag: "xyzzy"
 * 	ETag: W/"xyzzy"
 * 	ETag: ""
 * </p>
 * 
 * <h5 class='section'>See Also:</h5>
 * <ul class='doctree'>
 * 	<li class='extlink'><a class='doclink' href='https://www.w3.org/Protocols/rfc2616/rfc2616.html'>Hypertext Transfer Protocol -- HTTP/1.1</a>
 * </ul>
 */
public final class ETag extends HeaderString {

	/**
	 * Returns a parsed <code>ETag</code> header.
	 * 
	 * @param value The <code>ETag</code> header string.
	 * @return The parsed <code>ETag</code> header, or <jk>null</jk> if the string was null.
	 */
	public static ETag forString(String value) {
		if (value == null)
			return null;
		return new ETag(value);
	}

	private ETag(String value) {
		super(value);
	}
}
